The mammalian gut is a complex and diverse ecosystem colonized with hundreds of different bacterial species. The coevolution of humans with their intestinal microbiota has resulted in cooperative relationships that have shaped the biology and the genomes of these symbiotic partners. Little is known about the mechanisms used by the predominant members of the gut microbiota to establish symbiotic relationships in the human intestine. The experiments outlined in this proposal are designed to characterize a novel and abundant class of bacterial glycoproteins that are synthesized by the predominant bacteria of the mammalian intestine, namely the Bacteroides. These molecules are unique in many regards. First, they are the only bacterial glycoproteins demonstrated to contain L-fucose. Second, they represent the largest number of glycoproteins reported to be synthesized by bacteria. Lastly, their synthesis of involves a unique bacterial enzyme, synthesized only by the Bacteroides, to use fucose scavenged from host molecules. The experiments outlined in this proposal will address three aspects of fucosylated glycoproteins of Bacteroides. The goal of the first aim is to identify the fucosylated glycoproteins of B. fragilis and B. distasonis, and to characterize the glycan portion of these molecules. The goal of the second aim is to determine which fucosyltransferases and other gene products are involved in the synthesis and linkage of the glycans to the proteins. The goal of the third aim is to functionally characterize,.both in vitro and in vivo, the functions of these glycoproteins to the bacteria and their contribution to the symbiotic interaction with the host. Ultimately, these studies will allow us to better understand how these microorganisms are affecting the host with either beneficial (probiotics, immune regulation and tolerance, maturation of the epithelial surface) or deleterious (transfer of antibiotic resistance and involvement in inflammatory bowel disease) effects. B. fragilis is also an important opportunistic pathogen. B. fragilis predominates in intraabdominal abscesses and cases of anaerobic bacteremia, and has been isolated from patients with bone and soft tissue infections, and has been identified as a contributing factor to increased incidence of preterm labor. Therefore, the analysis of the fucosylated glycoproteins of B. fragilis will also contribute to our understanding of the pathogenic potential of this organism.